It has been a well known theory in the art that in order to attain stable braking action by causing both the front and rear wheels to decelerate at the same rate, the rate of increase in pressure of brake fluid to be supplied to rear-wheel cylinders from a master cylinder must be so controlled as to gradually reduce as compared with the rate of increase of pressure of brake fluid to be supplied to front-wheel cylinders. For this purpose, the conventional automotive brakes systems have incorporated in general deceleration sensitive brake fluid pressure control valves inserted in brake lines communicating the master cylinder and the rear-wheel cylinders. The deceleration-sensitive, brake fluid pressure control valves comprise in general a ball valve floatingly disposed within a valve chamber in communication with the master cylinder and the rear-wheel cylinders, and a differential piston whose free ends are exerted with the hydraulic pressure on the side of the master cylinder and the hydraulic pressure on the side of the rear-wheel cylinders, respectively. When the deceleration of an automotive vehicle reaches a predetermined value, the ball valve is caused to move forwardly by its own inertia to close the valve port, thereby interrupting the communication between the master cylinder and the rear-wheel cylinders and thereafter the hydraulic pressure on the side of the master cylinder is transmitted through the differential piston to the rear-wheel cylinders at a predetermined decreased ratio so that the hydraulic pressure in the rear-wheel cylinders may be increased at a decreased rate as compared with the pressure build-up in the front-wheel cylinders. Thus the hydraulic pressure in the rear-wheel cylinders increases at the same rate as in the front-wheel cylinders until the ball valve closes the valve port, and once the valve port has been closed the hydraulic pressure in the rear-wheel cylinders increases at a rate slower than in the front-wheel cylinders. As a result, a curve representative of the braking force distribution between the front and rear wheels has a flexing point at a position corresponding to the time when the valve port is closed with the ball valve and is therefore approximately similar to an idealized braking force distribution characteristic curve.
However delay in response to the ball valve; that is, a time interval between the time when the deceleration reaches a predetermined value and the time when the ball valve closes the valve port, is inevitable in the control valves of the type described above. As a result when the hydraulic pressure in the master cylinder rapidly increases a result of rapid or abrupt brake application, the hydraulic pressure in the rear-wheel cylinders also rapidly increases accordingly until the ball valve shifts to the valve closing position even after the deceleration has reached a predetermined value so that the flexing point in a braking force distribution curve appears at a higher pressure level as compared with the case when brakes are applied in the normal manner. As a consequence, the braking force distribution is by far departed from the idealized distribution so that the rear-wheels may be braked too much.